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83 lines
3.3 KiB
C
83 lines
3.3 KiB
C
#include <gtk/gtk.h>
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#include <epoxy/gl.h>
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/* A png for a red/yellow checkerboard */
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static const char image_data[] = {
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0211, 0120, 0116, 0107, 0015, 0012, 0032, 0012, 0000, 0000, 0000, 0015, 0111, 0110, 0104, 0122,
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0000, 0000, 0000, 0040, 0000, 0000, 0000, 0040, 0001, 0003, 0000, 0000, 0000, 0111, 0264, 0350,
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0267, 0000, 0000, 0000, 0006, 0120, 0114, 0124, 0105, 0377, 0000, 0000, 0377, 0340, 0000, 0241,
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0105, 0325, 0002, 0000, 0000, 0000, 0025, 0111, 0104, 0101, 0124, 0010, 0327, 0143, 0230, 0011,
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0004, 0014, 0151, 0100, 0000, 0041, 0300, 0334, 0101, 0044, 0006, 0000, 0355, 0275, 0077, 0301,
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0347, 0173, 0153, 0007, 0000, 0000, 0000, 0000, 0111, 0105, 0116, 0104, 0256, 0102, 0140, 0202
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};
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G_MODULE_EXPORT gboolean
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render_orange_glonly (GtkWidget *glarea,
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GdkGLContext *context)
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{
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GdkTexture *texture;
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GdkTextureDownloader *downloader;
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GBytes *bytes;
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gsize stride, width, height;
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GLuint tex_id, fb_id;
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gdk_gl_context_make_current (context);
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/* Clear to green, so that errors in the following code cause a problem */
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glClearColor (0.0, 1.0, 0.0, 1.0);
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glClear (GL_COLOR_BUFFER_BIT);
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/* load the checkerboard image */
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bytes = g_bytes_new_static (image_data, G_N_ELEMENTS (image_data));
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texture = gdk_texture_new_from_bytes (bytes, NULL);
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g_bytes_unref (bytes);
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width = gdk_texture_get_width (texture);
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height = gdk_texture_get_height (texture);
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downloader = gdk_texture_downloader_new (texture);
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/* Make sure we use a format that GLES does *NOT* support.
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* And that must include extensions.
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* But GL_EXT_texture_norm16 does support RGB16 as a source, which
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* is why we also use mipmaps below. */
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gdk_texture_downloader_set_format (downloader, GDK_MEMORY_R16G16B16);
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bytes = gdk_texture_downloader_download_bytes (downloader, &stride);
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g_object_unref (texture);
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gdk_texture_downloader_free (downloader);
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glGenTextures (1, &tex_id);
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glActiveTexture (GL_TEXTURE0);
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glBindTexture (GL_TEXTURE_2D, tex_id);
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/* Now load the image in this ideally unsupported format. Maybe
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* things fail already here. Usually they don't. */
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glTexImage2D (GL_TEXTURE_2D, 0, GL_RGB16,
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width, height,
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0, GL_RGB, GL_UNSIGNED_SHORT, g_bytes_get_data (bytes, NULL));
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g_bytes_unref (bytes);
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/* Generate mipmaps. GLES should give up now.
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* GL should turn the checkerboard into orange mipmap levels though.
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*/
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glGenerateMipmap (GL_TEXTURE_2D);
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glGenFramebuffers (1, &fb_id);
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glBindFramebuffer (GL_READ_FRAMEBUFFER, fb_id);
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/* Bind mipmap level 2 for reading, so we rely on properly converted
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* mipmaps. */
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glFramebufferTexture2D (GL_READ_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, tex_id, 2);
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/* On GLES, this should now fail due to incomplete framebuffer and
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* leave us with the green contents we've drawn above.
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* Or we are on GL, everything works perfectly, and we now get orange. */
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glBlitFramebuffer (0, 0,
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width / 4, height / 4,
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0, 0,
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gtk_widget_get_width (glarea) * gtk_widget_get_scale_factor (glarea),
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gtk_widget_get_height (glarea) * gtk_widget_get_scale_factor (glarea),
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GL_COLOR_BUFFER_BIT,
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GL_LINEAR);
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glDeleteFramebuffers (1, &fb_id);
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glDeleteTextures (1, &tex_id);
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return TRUE;
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}
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